In any time or location-displaced capture of image data, parameters may change that can affect the overall and/or regional color balance of the image. Temporal displacement changes may occur for reasons such as changes in exposure parameters (e.g., shutter speed, aperture, or ISO gain) or because of lighting changes during the time displacement. Location displacement (e.g., camera location, wherein multiple cameras capture either synchronously or asynchronously) may be the result of camera sensor response differences due to sensor, lens, and/or other factors. Typical applications involving time displacement include stereo capture with a single camera, panoramic scene capture, and general image bursts. Location displacement scenarios include stereo or multi-view camera rigs with multiple cameras, and separate scene captures with difference cameras (possibly at different times as well). In all of these cases, for viewing enjoyment, there is a high interest in color matching the images. For stereoscopic viewing, this may be important to minimize color discrepancies between the left and right eyes that can cause discomfort. For panoramic stitching and viewing, it may be important to have a smooth appearance of the stitched images over the course of the panorama. For editing of multiple captured images (such as in video splices), it may be important to the smooth transition between footage. These applications and others demonstrate the importance of the problem.
A common technique in addressing this problem is the use of per channel (R/G/B or other color map color channels) histogram measurement and equalization, either globally or within “binned” regions of an image (e.g., shadow, midtone, and highlight). Such techniques experimentally prove to be variable with regard to how well they address the problem described, and in many cases are unsatisfactory due to the channel responses not being independent. Complex techniques may create better results, but at the expense of extreme computation times for even relatively small images.
In view of the foregoing, it is desired to provide improved systems and techniques for image color matching and equalization.